Vacuum deposition is a common method for coating metals such as aluminum, copper, zinc, and tin onto various substrates of metal, glass and plastic. The metal is vaporized in a vessel commonly referred to as a "vaporization boat" by electric resistance heating. The boat is connected to a source of electrical power to heat the vessel to a temperature which will cause the metal charge in contact with the boat to vaporize. Typically, the product is placed in an evacuated chamber within which the metal is vaporized. The product may be fed individually or continuously into the chamber or, alternatively, may form part of the chamber itself. A wide variety of product is coated with metal using vapor deposition including ,e.g., television picture tubes, automobile headlights, toys and the like.
Resistance heated vaporization boats in use today are commonly made of intermetallic composite materials such as titanium diboride and boron nitride or titanium diboride, boron nitride and aluminum nitride. An alternative composition for a vaporization boat employs a coating of pyrolytic boron nitride which may be coated over the composite material or more particularly over a substrate material of graphite as taught in U.S. Pat. No. 4,264,803 the disclosure of which is herein incorporated by reference. In general the substrate is first fabricated into a rectangular shape which is then coated with the pyrolytic boron nitride. The opposite ends of the substrate are left exposed to permit the boat to be electrically connected in circuit with a power supply via a contact assembly or clamp. A boat fabricated from graphite has been found to be particularly susceptible to breakage at the uncoated ends which tend to break off during handling. The fragile nature of the boat makes it difficult to handle without exercising special precaution to avoid breakage.